Python pytz timezone function returns a timezone that is off by 9 minutes

Question

For some reason which I haven't been able to figure out yet, from the the following code:

>>> from pytz import timezone >>> timezone('America/Chicago') 

I get:

<DstTzInfo 'America/Chicago' LMT-1 day, 18:09:00 STD> 

When, I assume, I should get:

<DstTzInfo 'America/Chicago' LMT-1 day, 18:00:00 STD> 

...since I don't think that my timezone is 6 hours and 9 minutes away from UTC.

I have looked at the source code for pytz but I will admit that I haven't exactly been able to figure out what is going wrong.

I have passed other values to the timezone() function, and the values it returns appear to be correct. For some reason though, the information relevant to my timezone is not correct.

Finally, my co-worker in the cube next to me has confirmed that the function returns the correct timezone info on his machine.

Does anyone have any idea why my timezone ('America/Chicago') would be off by 9 minutes? I am running version 2015.7 of pytz installed using pip. Thank you!

Answer 1

Answer based on the answer by Carl Meyer in Google Groups Answer

The reason for this difference, is that this is NOT the right way of converting a timezone agnostic datetime object to a timezone aware object.

The explanation being:

"A pytz timezone class does not represent a single offset from UTC, it represents a geographical area which, over the course of history, has probably gone through several different UTC offsets. The oldest offset for a given zone, representing the offset from before time zones were standardized (in the late 1800s, most places) is usually called "LMT" (Local Mean Time), and it is often offset from UTC by an odd number of minutes."

(quote from the cited answer in Google Groups)

Basically, you should do:

from datetime import datetime import pytz  my_datetime = datetime(2015, 6, 11, 13, 30) my_tz = pytz.timezone('America/Chicago')     good_dt = my_tz.localize(my_datetime)  print(good_dt) 

out: 2015-06-11 13:30:00-05:00

Answer 2

Unless your local timezone has a fixed UTC offset then it is pointless to talk about its specific value without providing a specific date/time.

If you provide the time e.g., the current time then you'll see that pytz produces the expected UTC offset:

>>> from datetime import datetime >>> import pytz >>> datetime.now(pytz.timezone('America/Chicago')).strftime('%Z%z') 'CST-0600' 

See

• Datetime Timezone conversion using pytz
• pytz localize vs datetime replace

If you don't provide a specific date/time then pytz may return an arbitrary utc offset from the set of available utc offsets for the given timezone. The recent pytz versions return utc offsets that correspond to the earliest time (LMT as a rule) but you should not rely on it. You and your friend may use different pytz versions that may explain the difference in results.